CHROMOSOMES AND MITOCHONDRIA 277 



hour stage up to the three-days-nine-hour stage. 

 The cells of the earliest stage studied contained mito- 

 chondria (Fig. 76) which were differently arranged 

 in the germinal layers : the ectoderm and entoderm 

 cells contained, for the most part, rods and threads, 

 the granules being scarce, and the mesoderm cells 

 were characterized by numerous granules and few 

 rods and threads. At the three-day stage the mito- 

 chondria of the neuroblasts became difficult to 

 stain by the usual method, but did stain like neuro- 

 fibrils. These and other observations led Meves 

 to the conclusion that the mitochondria are of con- 

 siderable importance in cellular differentiation and 

 are in fact the bearers of hereditary Anlagen. 



Since this paper of Meves appeared, the zoological 

 periodicals have been flooded with the results of in- 

 vestigations of the mitochondria in almost every 

 sort of germ and somatic cell, both normal and 

 abnormal, and in PROTOZOA and METAZOA, IN- 

 VERTEBRATES and VERTEBRATES. No report on 

 spermatogenesis, oogenesis, or early embryonic de- 

 velopment is complete without reference to the mito- 

 chondria. In plants, also, cellular bodies have been 

 described of a mitochondrial nature (Meves, 1904 ; 

 Duesberg and Hoven, 1910; Guilliermond, 1911). 



A large number of new terms have been coined 

 for the purpose of describing these cytoplasmic in- 

 clusions. Some of them are as follows : (1) mito- 

 chondria, applied by Benda (1897, 1898) to certain 

 granules with definite staining reactions ; (2) chon- 

 driosomes, proposed by Meves (1908) for both single 



